The present invention relates to injection molding machines. More particularly, the present invention relates to the common control of multiple shooting pots in a injection molding machine.
Employing control units, such as shooting pots, to introduce thermoplastic resins or other materials into a mold cavity in an injection molding machine is well known. Generally, a primary resin source feeds the material to a shooting pot reservoir which is, in turn, operated to feed a measured, or metered, quantity of the material into the mold cavity. U.S. Pat. No. 3,516,123, entitled xe2x80x9cInjection Molding Machinexe2x80x9d, to Lang; and No. 3,231,656, entitled xe2x80x9cApparatus and Method of Plastic Moldingxe2x80x9d, to Ninneman both disclose the use of shooting pots to provide accurately metered shots of resin to a mold cavity. Metering permits an accurate amount of material to be injected into a mold to ensure that a properly formed part is created and to prevent waste of material in the form of xe2x80x9cflashxe2x80x9d, etc. due to overfilled molds. Metering is generally achieved by controlling the distance by which an injection plunger in the shooting pot is retracted and advanced for each shot.
Other metering techniques are also well known. For example, U.S. Pat. No. 4,966,545, entitled Staged Shooting Pot for Injection Molding, to Brown, shows how a single shooting pot can be operated to cause two sequential metered injections of the same resin into the same mold cavity. U.S. Pat. No. 4,460,324, to Van Appledom, entitled xe2x80x9cShot Cylinder Controller for Die Casting Machines and the Likexe2x80x9d, shows how the injection speed of the piston of shooting pot can be controlled, thereby controlling the rate of injection of the resin into the mold cavity.
It is also well known to supply thermoplastic material to a multicavity mold through a hot runner system. The hot runner system can include a plurality of shooting pots, with at least one shooting pot associated with each mold cavity.
Hot runners systems can also be used for multimaterial injection, or coinjection, molding. Typically, two or more resins are injected, either simultaneously or sequentially, into each mold cavity to produce multi-layered molded structures. For example, a common application for multimaterial molding is the production of food quality containers from recycled plastic. Government standards require that any surfaces which contact the food be made of new, virgin, plastic. To take advantage of lower cost recycled plastics, manufacturers use coinjection techniques to encapsulate recycled material in a sheath of new plastic. U.S. Pat. No. 5,098,274 to Krishnakumar, entitled xe2x80x9cApparatus for Injection Molding of Multilayer Preformsxe2x80x9d, and U.S. Pat. No. 4,717,324 to Schad, entitled xe2x80x9cCoinjection of Hollow Articles and Preformsxe2x80x9d both disclose injection molding machines for multimaterial applications.
Generally, individual control of the shooting pot strokes is provided in these prior art injection molding machines. Separate hydraulic actuation cylinders for each shooting pot injection plunger are mounted inside the machine""s stationary platen. These hydraulic cylinders must be individually set for stroke to control the individual metering of the resins into the mold cavities. The setting of the cylinders can be a hazardous operation, which is performed manually and requires personnel to reach into the machine amongst the heated injection nozzles, close to hot surfaces and heated injection materials. Furthermore, the molding process has to be interrupted for this adjustment, which can cause significant loss of production time, especially in larger machines having up to ninety six injection plungers.
U.S. Pat. No. 4,632,653 to Plocher, entitled xe2x80x9cPress with a Plurality of Injection Plungersxe2x80x9d describes a common actuator for the injection plungers in a transfer molding machine. The injection plungers are actuated by a hydraulic drive acting on a single crosspiece. However, the shooting pot actuator disclosed in Plocher has several limitations and disadvantages which make it inapplicable to metered injection molding machines. Firstly, the shooting pots in a compression molding machine do not provide metered shots. Instead, each shooting pot is filled with an approximate amount of resin, and the injection pistons are actuated by the crosspiece to compress the resin into the mold cavity. Plocher discloses pressure compensating pistons and overflow channels to relieve the mold cavities in the case of overfilling, which results in non-uniform product and flashing. Also, there is no mechanism provided for adjusting the stroke of the injection pistons since precise control of the amount of resin injected into the mold is not critical in such a transfer molding process. Second, the crosspiece actuator in Plocher is located within the mold, which increases the cost of designing and manufacturing the mold. Also, such a design is impractical in machines with high clamp forces as the volume occupied by the crosspiece reduces the strength of the mold component in which it is located, thus increasing the likelihood of deformation of mold components when clamped. Further, the mold must be completely disassembled to obtain access for maintenance, adjustment, or replacement.
An injection molding machine comprising:
a mold having at least two mold cavities;
at least one shooting pot, each said shooting pot fluidly communicating with at least two of said mold cavities, said shooting pot having an injection plunger for expressing an injectable material from said shooting pot into said at least two of said mold cavities;
a clamp unit for clamping said mold, said clamp unit including a stationary platen and a moveable platen disposed on opposite sides of said mold;
an extruder for supplying said material to each said shooting pot, said extruder fluidly communicating with said mold cavity through said shooting pots;
a shooting pot actuator connected to at least one of said shooting pots, each said shooting pot actuator being disposed exterior to said clamping unit and extending through one of said platens, each said shooting pot actuator including at least one pusher having (i) a retracted position limiting movement of a respective of said injection plungers as each said shooting pot is charged, and (ii) moveable to a second position to advance said respective of said injection plungers and express a metered amount of material from said shooting pots;
a linear position sensor operably attached to a control system, for sensing each said actuator; and,
a drive means responsive to said control system and operable to move said at least one pusher between said retracted and second positions.
A multimaterial injection molding machine comprising:
a mold having at least two mold cavities, each of said at least two mold cavities having at least a first and a second shooting pot communicating therewith and with at least one other of said mold cavities, said first and second shooting pots having respective first and second injection plungers;
a clamp unit including a stationary platen and a moveable platen disposed on opposite sides of said mold;
an injection unit for supplying to said shooting pots material to be injected;
a shooting pot actuator, exterior to said clamping unit and extending through one of said platens, said actuator having a first group of pushers for abutting said first injection plungers, and a second group of pushers for abutting said second injection plungers; and,
a drive means operable to move said first and second groups of pushers between a first position and a second position, wherein in said first position said injection plungers limit the volume of material which each said shooting pot can receive from said injection unit, and wherein said material is expressed from said shooting pots as said actuator is moved to said second position.
A multimaterial injection molding machine having a mold with at least two mold cavities, each said mold cavity communicating with a shooting pot for charging with an injectable material, and each said shooting pot having an injection plunger for expressing said material from said shooting pot into at least two of said mold cavities, a clamp unit for clamping said mold, said clamp unit including a stationary platen and a moveable platen disposed on opposite sides of said mold, and an injection unit for supplying said material to said shooting pots, comprising:
a frame securable to an exterior of said stationary platen and having a portion spaced from said stationary platen;
a shooting pot actuator, supported for linear movement within said frame, for extension through one of said platens to abut said injection plungers, said shooting pot actuator having a first position limiting rearward movement of said injection plungers as said shooting pot is charged, and moveable to a second position to advance said injection plungers and express a metered amount of material from said shooting pots;
a linear position sensor mounted on said frame and operably attached to a control system for sensing said actuator; and,
a drive mounted on said portion, said drive being responsive to said control system and operable to move said actuator between said first and second positions.
A shooting pot actuator for a multimaterial injection molding machine having a clamp unit including a stationary platen and a moveable platen disposed on opposite sides of a mold, having at least two mold cavities and at least first and second shooting pots each communicating, with at least two of said mold cavities, said shooting pots having corresponding first and second injection plungers, and an injection unit to provide to said shooting pots material to be injected, comprising:
a first set of at least two first pushers, each said first pusher is extending through one of said platens and operable to abut a respective first injection plunger;
a second set of at least two second pushers mounted on a plate through which said first pushers extend, each said second pusher is operable to abut a second injection plunger;
said first and second sets each having an adjustable first position limiting rearward movement of their respective injection plungers as said shooting pots are charged with said material, and moveable to a second position to advance their respective injection plungers and express a metered amount of material from said shooting pots, said first and second sets being operable to move independently between said first and second positions.